New formulas for iCa estimation over a wide range of serum albumin concentrations measured by a modified bromocresol purple method

DOI
  • Ishigaki Takuya
    Department of Clinical Chemistry and Laboratory Medicine, Kyushu University Hospital
  • Kameda Akari
    Department of Clinical Chemistry and Laboratory Medicine, Kyushu University Hospital
  • Ichinari Hayato
    Department of Clinical Chemistry and Laboratory Medicine, Kyushu University Hospital
  • Yamada Shunsuke
    Department of Medicine and Clinical Science, Graduate School of Medical Sciences, Kyushu University
  • Fujisaki Kiichiro
    Department of Medicine and Clinical Science, Graduate School of Medical Sciences, Kyushu University
  • Nakano Toshiaki
    Department of Medicine and Clinical Science, Graduate School of Medical Sciences, Kyushu University
  • Hotta Taeko
    Department of Clinical Chemistry and Laboratory Medicine, Kyushu University Hospital
  • Kang Dongchon
    Department of Clinical Chemistry and Laboratory Medicine, Kyushu University Hospital Department of Clinical Chemistry and Laboratory Medicine, Kyushu University, Graduate School of Medical Sciences

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説明

  Although the serum calcium concentration is affected by the serum albumin concentration and requires use of a formula, previous formulas were constructed using the bromocresol green (BCG) method, which has problems with accuracy. In this study, we constructed a new calcium formula using a modified bromocresol purple method, which overcame the limitations of the BCG method. The new formulas were constructed with the pH, ionized calcium (iCa), calcium, and albumin values of 706 patients. Sensitivity, specificity, and weighted kappa coefficient were evaluated with the values of 50 hemodialysis patients. We developed three formulas: to estimate iCa directly (Formula 1), to estimate iCa corrected to pH 7.4 (Formula 2), and to evaluate iCa corrected to pH 7.4 as an index (Formula 3). Using hemodialysis patients for validation, Pre-correction calcium and Formula 1 were tended to be classified as hypocalcemia than iCa or iCa corrected to pH 7.4, while Payne's formula and Kidney Disease Outcomes Quality Initiative's formula 2 were tended to be classified as hypercalcemia. Based on the weighted kappa coefficient, Formula 3 as corrected calcium was the best for assessment of calcium conditions. Since the serum calcium is widely used in daily practice, Formula 3 may be the most useful.

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